3. cooling a. introduction 1) definition reduce temperature of air entering greenhouse why?...

3. Cooling

a. Introduction

1) Definition• reduce temperature of air entering

greenhouse• Why?–Reduce stress–Uniformity–Better growth

2) Types of systems

a) refrigeration system

b) evaporative cooling

• pad and fan

• high pressure mist - fog

b. Evaporative/cooling

Evaporative cooling

1) Principal– Energy Required

– H2O (liquid) + Warm air (energy) > H2O (gas) + cooler air

– 1000 BTU to change 1 lb liquid H2O to gas (water vapor)

2) Factors determining cooling– Temperature: outside

air– Relative humidity:

outside air– Temperature: inside

air– air movement– shading– structure– Covering

Evaporative Cooling

c. Pad and fan system

– 80% to 90% of difference

between wet and dry

bulb

– Temp increases from

inlet to outlet

– higher moisture

(outside) reduces temp

decrease

80% to 90% of difference between wet and dry bulb

Cooling efficiency

1) design of system

• pad and fan system

– Equipment

• Separate house

• Ridge and

furrow

– Fan and pad size

• fans, same as

for ventilation

– pads, based on fan

size and material

2) Important points in operation

– Eliminate leaks • through pads • around pads • other areas

– Uniform wetting • holes clogged • Detergent

– Algae • CuSO4

d. Unit coolers

e. High pressure mist - fog

– Small droplets• Nozzles

– 150-200 psi up to 500 psi

– special pump

– Problems• salt deposits• poor air movement

Fog evaporative cooling

Compare pad and fan to fog cooling